Postal service
There’s no “official” postal service in the Realms, with stamps and uniforms and suchlike, but all peddlers, minstrels, caravan wagon-merchants, trading coster offices, and caravan masters have traditionally taken verbal messages, written messages, and small packages (usually a canvas ‘purse’ sewn together and sealed against damp with pitch or sap before being sewn inside a second layer of canvas) for delivery to distant places, in return for quite steep fees (so common folk use such means only in emergencies). The cost reflects the fact that the delivery person may pay someone else, partway along the route, to do the last leg of the delivery, and still wants to make a few coins of profit after doing this. It would be rare to find any tangible message being delivered for less than a 6 gp ‘up front’ charge, unless it’s “just to the next village or two along” a shared road. Heralds and court envoys regularly deliver official messages and royal communications, of course. All priesthoods maintain a regular message service between temples (and can use spells to deliver short verbal messages ‘directly’), and often offer a cut-rate service to faithful worshippers (who have already given regular or substantial offerings to the temple) for including their messages along with the temple reports, written prayers and sermons, and holy decrees. Lastly, shippers of large cargoes will often make several copies of a message for their intended recipient, and slip it inside crates or coffers that are then closed and sealed. Sometimes these are of the “If the finder of this delivers it unopened to Durth Merrilees of Merrilees Tapestries on the Way of the Dragon, Durth will pay a reward of 4 dragons” variety (this example obviously being for a message inbound to Waterdeep). Note that this can take some time, and many messages never arrive. Note also that there’s really no such thing as privacy unless codes are used, because in many cases a ‘local village scribe’ does the initial writing for the sender, and anyone can open and read (or even alter) the message en route. Many folk employ ‘private codes’ of this sort: plain everyday writing, but certain phrases have a previously-arranged ‘private meaning’ (example: “Aunt Maerl continues to do well, and asks after you” really means: “Our investment scheme is flourishing, and that extra money you offered to put into it is now needed”) There are armed, experienced, mounted couriers within Cormyr and Sembia (operating only within the boundaries of those countries), because there’s enough wealth and population density to support such services. They typically deliver small packages swiftly and reliably, in return for 25 gp or more fees. As for the general spread of information (news and rumors), it spreads by priests spell-talking to distant priests, via ‘wandering’ peddlers and minstrels and the Harpers, via trading costers, and with every ship and caravan (alert readers of my accounts of the Realms from 1979 onwards should recall what THO knows well: every arrival of a caravan to stay the night at the Old Skull spurred most of Shadowdale to turn out to “hear the latest” news). There are even newspapers (“broadsheets”) published in many cities (see my Realmslore WotC website column for some details of those printed in Waterdeep), and these travel with all of the above. The arrival of a ‘new’ (sometimes seasons-old) broadsheet in a remote village is cause for a social gathering at the local tavern for the best reader to entertain everyone for an evening.